1. Field of Invention
Embodiments of the present invention are related to audio processing, and more particularly to control of an analog-to-digital converter.
2. Related Art
Conventionally, wireless communication reception in mobile devices requires use of high performance receivers that comply with stringent power consumption constraints. A receiver for broadcast services is expected to provide reliable reception under multiple channel impairments such as multi-path fading, Doppler shift, and additive noise. A high performance implementation of the receiver can achieve significant improvement of reception range and indoor coverage. Communication and broadcast systems which use terrestrial transmitters have particularly high requirements for receiver performance. A transmission band is often populated with an ensemble of high power broadcast transmission of terrestrial analog TV and radio, as well as aeronautical and governmental transmissions. Receivers receiving terrestrial broadcast signal are typically required to handle a large dynamic range of both a signal of interest and signals in adjacent channels.
In a digital receiver implementation, an analog signal at a tuner output is sampled by an analog-to-digital converter (ADC). The sampled signal is then demodulated by a digital signal processing means. The analog signal at the tuner output typically contains the signal of interest, as well as undesired signals coming from adjacent channels. These undesired signals may have very high power relative to the signal of interest.
There are several methods that receivers can use to handle the large dynamic range of the received signals. One such method is to implement analog selectivity filters. These analog selectivity (i.e., band selective) filters are centered on a channel of interest and reject adjacent channels. A drawback of such a design is complexity of the analog filter design. In order to provide high selectivity, the filters need to be of high order (i.e., incorporate multiple zeros and poles) thus requiring a plurality of components such as amplifiers, capacitors, resistors, and inductors. This is particularly prohibitive for silicon tuner design where the filter consumes a large silicon area, and therefore increases chip cost.
Another approach to handling adjacent channels is to sample the received signal using an analog-to-digital converter (ADC), and filter the adjacent channels using digital filters. Digital filters can be designed to be very sharp and very small in chip area. The challenge in such an approach is to have an ADC with sufficient resolution to accommodate a dynamic range of the channel of interest and the adjacent channels. Additionally, a high resolution ADC consumes much more power than an ADC with less resolution.
Therefore, there is a need for a receiver system capable of handling high power adjacent channels. There is also a need for a receiver system with low average power consumption, particularly for mobile and handheld devices.